The interaction of purified calf thymus RNA polymerase II and SV40 or adenovirus DNA have been examined. The enzyme binds to the DNA at specific sequences, but these sequences are not identical to the 5' start sites used in vivo or in vitro in a system containing a crude cell free extract. The enzyme also binds to nicks in DNA and forms the transcript which is an RNA-DNA adduct. During chain growth, the enzyme pauses or terminates RNA chains at specific sites.